Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C9/00—Alloys based on copper
  • C22C9/04—Alloys based on copper with zinc as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/08—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of copper or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working

Definitions

• the present invention relates to a free-cutting copper alloy casting having good castability, good dezincification corrosion resistance, excellent machinability, and a significantly reduced lead content, and a method for producing the free-cutting copper alloy casting.
• the present invention relates to a free-cutting copper alloy casting used in appliances and parts used for drinking water consumed daily by humans and animals, appliances and parts used in sanitary facilities such as kitchens, baths, and toilets, musical instruments, tableware, drainage appliances and parts, industrial piping parts, machine parts, sliding parts, medical parts, automobile parts, electric and home appliance parts, pressure vessels, building metal fittings, instrument parts, daily necessities, stationery, toys, and parts related to liquids and gases such as drinking water, industrial water, wastewater, and hydrogen, and a method for producing the free-cutting copper alloy casting.
• Specific part names include water faucets, water supply taps, mixer taps, stop valves, valves, joints, stems, cocks, water meters, drain plugs, pressure reducing valves, valve seats, gate valves, fire hydrants, gears, flanges, diverter valves, faucet valves, ball valves, bends, bearings, sleeves, connectors, and the like, and the present invention relates to free-cutting copper alloy castings used for these parts that are subjected to cutting, and to a manufacturing method for free-cutting copper alloy castings.
• This application claims priority based on Japanese Patent Application No. 2023-075579 filed in Japan on May 1, 2023 and Japanese Patent Application No. 2023-173342 filed in Japan on October 5, 2023, the contents of which are incorporated herein by reference.
• Cu-Zn-Pb alloys (so-called free-cutting brass rods, forging brass, and casting brass) or Cu-Sn-Zn-Pb alloys (so-called leaded red brass), which have excellent machinability, have generally been used for appliances and parts relating to drinking water and sanitation facilities, automobile parts, electrical and home appliance parts, machine parts, stationery, instrument parts, medical parts, and appliances and parts relating to liquids and gases such as industrial water, wastewater, and hydrogen, specifically names for these appliances and parts include water faucets, supply taps, mixer taps, stopcocks, valves, cocks, joints, valves, water meters, and connectors.
• the composition of the Cu-Zn-Pb alloy is, for example, 56 to 70 mass% Cu, 1 to 4 mass% Pb, and the balance is Zn
• the composition of the Cu-Sn-Zn-Pb alloy is, for example, 80 to 88 mass% Cu, 1 to 8 mass% Sn, 1 to 8 mass% Pb, and the balance is Zn.
• the European ELV Directive and RoHS Directive allow for a Pb content of up to 4 mass% in free-cutting copper alloys as an exception, but as in the drinking water field, there is active discussion about strengthening regulations on Pb content, including the elimination of exceptions.
• Cu-Zn-Bi alloys and Cu-Zn-Bi-Se alloys which contain Bi, which has machinability, in place of Pb, and in some cases, Se together with Bi;
• Cu-Zn alloys which contain a high concentration of Zn and increase the amount of ⁇ phase to improve machinability;
• Cu-Zn-Si alloys and Cu-Zn-Sn alloys which contain a large amount of ⁇ phase or ⁇ phase, which have excellent machinability, in place of Pb; and (4) Cu-Zn-Sn-Bi alloys which contain a large amount of ⁇ phase and also contain Bi.
• Patent Document 1 0.7 to 2.0 mass% of Sn and 0.5 to 2.0 mass% of Bi are added to a Cu-Zn alloy containing 59.5 to 66.0 mass% of Cu to precipitate a ⁇ phase, thereby improving corrosion resistance and machinability.
• Patent Document 2 a large amount of Bi, 0.3 to 4 mass%, preferably 1.8 to 3.2 mass%, is added to a Cu-Zn alloy containing 59 to 62 mass% Cu. Furthermore, since the ⁇ phase has poor dezincification corrosion resistance, the ⁇ phase is reduced and annealed at 350 to 550°C to separate the ⁇ phase with the ⁇ phase, thereby improving machinability and dezincification corrosion resistance. Thus, the ⁇ phase of Cu-Zn alloys has traditionally been poor in dezincification corrosion resistance, and as an improvement measure, it has been essentially necessary to reduce the ⁇ phase and anneal to separate the ⁇ phase with the ⁇ phase.
• Patent Documents 3 to 9 have proposed Cu-Zn-Si alloys containing Si instead of Pb as free-cutting copper alloys.
• Patent Documents 3 to 8 the Cu content is roughly 58 to 65 mass%, the Si content is roughly 0.2 to 1.5 mass%, and it is said that machinability is improved by the presence of Si contained in the ⁇ phase and fine P compounds formed by P and Zn, etc., and the area ratios of the ⁇ phase and ⁇ phase are specified, and excellent machinability is realized by the presence of P compounds and a small amount of Pb.
• Patent Document 2 it is a well-known fact that the ⁇ phase of a Cu-Zn alloy has poor dezincification corrosion resistance and further poor stress corrosion cracking resistance.
• Patent Documents 3 to 8 do not disclose any specific data related to dezincification corrosion resistance and stress corrosion cracking resistance, and it is presumed that the dezincification corrosion resistance and stress corrosion cracking resistance, which are technical issues with the ⁇ phase of conventional Cu-Zn alloys, have not been improved.
• Patent Document 9 specifies the total area of the gamma and kappa phases, which are formed from an alloy with high Cu and Si concentrations and have excellent machinability, with a Cu content of 71.5 to 78.5 mass% and a Si content of 2.0 to 4.5 mass%, and achieves excellent machinability with a small Pb content of 0.02 mass% or less. It also specifies that the Sn and Al content each is 0.1 mass% or more, which results in the formation of a large amount of gamma phase, further improving machinability and corrosion resistance.
• a Cu-Zn-Sn alloy contains small amounts of Si, Pb, P, or Fe, and contains 0.5 mass% or less of Pb, and by devising a manufacturing method, Pb-enriched particles are dispersed in the matrix, and the number density of the Pb-enriched particles present inside the ⁇ phase is increased, thereby obtaining excellent machinability.
• a finishing heat treatment at 400 to 600°C is essentially required to improve dezincification corrosion resistance.
• Patent Document 11 relates to a technique for producing a near-net hollow hot forged product using a hollow material in a Cu-Zn-Si-Pb-P alloy, and proposes a copper alloy in which the area ratios of the ⁇ , ⁇ and ⁇ phases are limited.
• Patent Document 12 proposes a copper alloy casting in which Si, Pb, Sn, and Bi are selectively contained in a Cu-Zn-Zr-P alloy, and the crystal grains are refined by the action of Zr and P.
• Patent Document 13 proposes a Cu-Zn-Sn-Al alloy that selectively contains Si and Pb and has a limited area ratio of the ⁇ phase and the ⁇ phase, thereby providing a copper alloy with excellent resistance to discoloration.
• Patent Document 14 proposes a copper alloy casting that does not contain Pb in a Cu-Zn-Si-Sn-Al-P alloy.
• Patent Document 15 proposes that in a Cu-Zn-Si-Sn-Al alloy, the apparent Zn content is important for improving the corrosion resistance, and proposes a copper alloy that substantially contains a large amount of Pb or Bi to improve machinability.
• Patent Document 16 describes a Cu-Zn-Si alloy that contains 65 mass% or more of Cu, has good castability and mechanical strength, and is a Pb-free copper alloy casting, and is said to have improved machinability due to the ⁇ phase. It also describes an example in which the alloy contains large amounts of Sn, Al, Mn, Ni, and Sb.
• Patent Documents 1 to 16 no substantial improvement has been found in the past with respect to the dezincification corrosion resistance of the ⁇ phase present in Cu-Zn alloys, which has traditionally been a major technical issue. Furthermore, there has been no disclosure of a Cu-Zn alloy that contains less than 0.2 mass% Pb and Bi and exhibits low cutting resistance and excellent machinability when cut at high speeds of over 100 m/min, even without the inclusion of Bi.
• the present invention has been made to solve the problems of the prior art, and aims to provide a free-cutting copper alloy casting that has excellent machinability and castability, good dezincification corrosion resistance despite containing a large amount of ⁇ phase ( ⁇ 1 phase, described below), high strength, good impact properties, and a significantly reduced lead content, as well as a method for manufacturing the free-cutting copper alloy casting.
• the present inventors conducted extensive research and obtained the following findings.
• the ⁇ phase includes the ⁇ ' phase
• the ⁇ phase includes the ⁇ ' phase
• the ⁇ phase includes the ⁇ ' phase.
• the ⁇ 1 phase refers to a modified ⁇ phase, and is distinguished from the ⁇ phase and the ⁇ 1 phase.
• the ⁇ 1 phase is characterized in that when hydrogen peroxide and aqueous ammonia are used as etching solutions and observed under a metallurgical microscope, a grain boundary pattern is observed in the ⁇ 1 phase and is recognized as a grain boundary.
• the ⁇ phase present in general Cu-Zn alloys, Cu-Zn-Bi alloys, Cu-Zn-Si alloys, etc. does not show a grain boundary pattern, i.e., a grain boundary, in the ⁇ phase even when etched with hydrogen peroxide and aqueous ammonia. Therefore, the ⁇ phase and the ⁇ 1 phase can be clearly distinguished.
• FIG. 1A which will be described later, shows the metal structure of the alloy of the present invention, which is composed of two phases, the ⁇ 1 phase modified from the ⁇ phase and the ⁇ phase, and a grain boundary pattern can be observed in the ⁇ 1 phase.
• FIG. 1A is referred to as a crystal grain boundary, and may also be simply referred to as a grain boundary.
• FIG. 2A is a metal structure of a comparative alloy consisting of a ⁇ phase and an ⁇ phase, and no grain boundary pattern is observed in the ⁇ phase, i.e., no grain boundary exists.
• P compounds refer to compounds of P and mainly Zn and/or Si.
• Cold workability refers to performance in cold processing such as drawing, wire drawing, crimping, and bending.
• Good or excellent machinability refers to low cutting resistance and good chip breakability during peripheral cutting using a lathe, unless otherwise specified.
• Conductivity refers to electrical conductivity, thermal conductivity, and electrical conductivity.
• Cooling rate refers to the average cooling rate in a certain temperature range.
• the cooling rate at a certain temperature for example, 500°C, is the cooling rate when passing through 500°C from a temperature just above 500°C, and is the average cooling rate from a temperature several tens of degrees higher than 500°C to 500°C.
• Commercial operation means manufacturing in actual mass production facilities.
• Patent Document 9 it is said that in a Cu-Zn-Si alloy, the ⁇ phase hardly contributes to the machinability of the copper alloy, but rather impedes it.
• Patent Documents 11, 12, and 13 the amount of the ⁇ phase is also significantly limited.
• Patent Document 2 as a method for improving the dezincification corrosion resistance of the ⁇ phase, a process of annealing at 350 to 550°C is required to reduce the ⁇ phase and to divide the ⁇ phase with the ⁇ phase.
• the ⁇ phase contains more Sn than Si in order to improve the dezincification corrosion resistance of the ⁇ phase, and that the alloy is heated to a temperature of 700 to 850°C, hot extruded, and held at 400 to 600°C as a finishing heat treatment for 30 minutes or more, with an average cooling rate of 0.2 to 10°C/sec from 400 to 200°C.
• Patent Documents 3 to 8 it was discovered that in a Cu-Zn-Si alloy, the inclusion of a certain amount of Si in the ⁇ phase has a significant effect on the machinability of the ⁇ phase itself. It is then said that the presence of fine P compounds, the inclusion of a small amount of Pb, and in some cases Bi, act synergistically to provide the alloy with excellent machinability. However, in order to provide the presence of P compounds, it is preferable to provide an average cooling rate of about 0.1°C/min to about 70°C/min in the temperature range from about 530°C to about 450°C after hot working or casting. However, Patent Documents 3 to 8 do not disclose data related to dezincification corrosion resistance and stress corrosion cracking resistance.
• the present inventors further worked on modifying the ⁇ phase itself in Cu-Zn-Si alloys.
• the modified ⁇ phase i.e., the ⁇ 1 phase
• an alloy containing the ⁇ 1 phase instead of the ⁇ phase could further increase strength without impairing ductility.
• This ⁇ 1 phase is obtained by first dissolving Si and P in the ⁇ phase at high temperatures after solidification, and then maintaining the ⁇ phase at a high temperature above 500°C, i.e., above 500°C and below 700°C, and increasing the cooling rate when cooling to room temperature, thereby bringing the state of the metal structure at high temperatures down to room temperature.
• the ⁇ 1 phase can be easily distinguished and differentiated from the ⁇ phase of Cu-Zn alloys.
• the surface is polished to a mirror finish and etched with a mixture of hydrogen peroxide and aqueous ammonia.
• aqueous solution of 3 mL of 3 vol% hydrogen peroxide and 22 mL of 14 vol% aqueous ammonia is used.
• the condition for obtaining the ⁇ 1 phase is that the molten metal is poured into a mold, and the casting after solidification is kept in a high-temperature ⁇ phase above 500°C, i.e., above 500°C and below 700°C, and brought to room temperature.
• the cooling treatment is preferably started at a temperature lower than 700°C and higher than 500°C, and when the temperature of the casting reaches 500°C, i.e., in the temperature range just above 500°C, it is required that the casting is cooled at a cooling rate of more than 300°C/min, and in the subsequent cooling treatment, the average cooling rate in the temperature range from 500°C to 300°C is at least more than 300°C/min.
• the cooling treatment refers to the manipulation of the cooling rate by water cooling or a similar method, rather than natural cooling.
• Patent Documents 3 to 8 in order to obtain fine compounds containing P, the casting or hot-worked material needs to be cooled at an average cooling rate of about 0.1° C./min to about 70° C./min in the temperature range from about 530° C. to about 450° C. after casting or hot working, slower than that of the present application, in which the average cooling rate is from about 0.1° C./min to about 70° C./min.
• the present application and Patent Documents 3 to 8 are moving in opposite directions in terms of cooling after solidification or hot working.
• the machinability of the Cu-Zn-Si alloy is significantly improved even without P compounds.
• the synergistic effect of the ⁇ 1 phase and a small amount of fine Pb particles or particles containing Pb and Bi reduces the cutting resistance and promotes chipping, so that good machinability is maintained even in high-speed cutting.
• the dezincification corrosion resistance and stress corrosion cracking resistance which were major unsolved issues of the conventional ⁇ phase, are significantly improved and solved by modifying the ⁇ phase to the ⁇ 1 phase.
• the mechanical properties inherit the high strength of the conventional ⁇ phase, and by modifying the ⁇ phase to the ⁇ 1 phase, the ductility and impact properties are not impaired, and the strength is higher.
• cold working such as caulking is rarely performed, and it is necessary for the castings to be non-brittle, i.e., to withstand impact, in terms of their applications.
• By modifying the ⁇ phase to the ⁇ 1 phase it is possible to prevent a decrease in impact properties while providing higher strength.
• the inventors have invented a copper alloy casting that has free-cutting performance comparable to that of conventional free-cutting brasses containing a large amount of Pb, and has better dezincification corrosion resistance and stress corrosion cracking resistance, higher strength, and better impact properties than conventional free-cutting brasses.
• a free-cutting copper alloy casting according to a first aspect of the present invention contains Cu from more than 60.5 mass% to less than 65.0 mass%, Si from more than 0.50 mass% to less than 1.20 mass%, Pb from 0.002 mass% to less than 0.20 mass%, P from more than 0.01 mass% to less than 0.18 mass%, and contains Bi as an optional element from 0.0001 mass% to less than 0.20 mass%, with the balance being Zn and inevitable impurities, wherein the total content of Fe, Mn, Co and Cr among the inevitable impurities is less than 0.50 mass%, and the content of Al is less than 0.30 mass%, the content of Cu is [Cu] mass%, the content of Si is [Si] mass%, and the content of P is [P] mass%.
• a free-cutting copper alloy casting according to a second aspect of the present invention contains 61.5 mass% or more and 64.8 mass% or less of Cu, 0.65 mass% or more and 1.10 mass% or less of Si, 0.003 mass% or more and less than 0.10 mass% of Pb, and 0.03 mass% or more and 0.15 mass% or less of P, and contains 0.001 mass% or more and less than 0.10 mass% of Bi as an optional element, with the balance being Zn and inevitable impurities, wherein the total content of Fe, Mn, Co and Cr among the inevitable impurities is less than 0.35 mass%, and the content of Al is less than 0.15 mass%, the content of Cu is [Cu] mass%, the content of Si is [Si] mass%, and the content of P is [0.03 mass% or more and less than 0.15 mass%.
• the free-cutting copper alloy casting of embodiment 3 of the present invention contains more than 60.5 mass% and less than 65.0 mass% Cu, more than 0.50 mass% and less than 1.20 mass% Si, 0.002 mass% or more and less than 0.20 mass% Pb, more than 0.01 mass% and less than 0.18 mass% P, and more than 0.05 mass% and less than 0.70 mass% Sn, and contains 0.
• the steel sheet contains 0.0001 mass% or more and less than 0.20 mass% Bi, with the balance being Zn and inevitable impurities, and among the inevitable impurities, the total content of Fe, Mn, Co and Cr is less than 0.50 mass%, and the Al content is less than 0.30 mass%, the Cu content is [Cu] mass%, the Si content is [Si] mass%, and the Pb content is [Pb] mass%.
• the free-cutting copper alloy casting of aspect 4 of the present invention is characterized in that, in any one of aspects 1 to 3 of the present invention, it is used for appliances and parts relating to drinking water and sanitation facilities, water meters, valves, drainage appliances and parts, industrial piping parts, automobile parts, electrical and home appliance parts, machine parts, stationery, toys, musical instruments, sliding parts, instrument parts, and medical parts.
• the manufacturing method of the free-cutting copper alloy casting of aspect 5 of the present invention is a manufacturing method of the free-cutting copper alloy casting of any one of aspects 1 to 4 of the present invention, which includes a casting process, and is characterized in that in the cooling process of the final casting process, the cooling rate at the time when the temperature of the casting is 500°C exceeds 300°C/min, and the average cooling rate in the temperature range from 500°C to 300°C exceeds 300°C/min.
• the manufacturing method of the free-cutting copper alloy casting of aspect 6 of the present invention is a manufacturing method of the free-cutting copper alloy casting of any one of aspects 1 to 4 of the present invention, which includes a casting step, and is characterized in that in the cooling process of the final casting step, the cooling treatment start temperature is higher than 500°C and lower than 700°C, the cooling rate at the time when the temperature of the casting is 500°C exceeds 300°C/min, and the average cooling rate in the temperature range from 500°C to 300°C exceeds 300°C/min.
• the manufacturing method of the free-cutting copper alloy casting of aspect 7 of the present invention is a manufacturing method of the free-cutting copper alloy casting of any one of aspects 1 to 4 of the present invention, which includes a casting step and a heat treatment step, and is characterized in that in the final heat treatment step, the casting is heated at a temperature higher than 520°C and lower than 650°C for 1 minute to 5 hours, and in the cooling treatment step after the heat treatment, the cooling treatment is started at a temperature where the temperature of the casting exceeds 520°C, the cooling rate at the time when the temperature of the casting reaches 500°C exceeds 300°C/min, and the average cooling rate in the temperature range from 500°C to 300°C exceeds 300°C/min.
• a free-cutting copper alloy casting that has excellent castability, good machinability, dezincification corrosion resistance, and stress corrosion cracking resistance, high strength, an excellent balance of strength, impact properties, and ductility, and has a significantly reduced Pb content, and a method for producing the free-cutting copper alloy casting.
• Alloy No. S02 has a composition of Zn-62.9 mass% Cu-0.94 mass% Si-0.082 mass% P-0.067 mass% Pb-0.03 mass% Sn.
• the molten metal is poured at 1080°C and cast into a sand mold, removed from the sand mold at 650°C, and a cooling treatment is started at 560°C, with an average cooling rate of 900°C/min in the temperature range from 550°C to 500°C, and an average cooling rate of 900°C/min in the temperature range from 500°C to 300°C.
• 1B is a cross-sectional metal structure photograph including a portion exhibiting maximum corrosion depth, showing the results of a dezincification corrosion test performed on the alloy casting of FIG. 1A in accordance with the ISO 6509 test method.
• 1 is a photograph of the structure of a copper alloy casting according to an embodiment, the copper alloy casting being obtained by subjecting Alloy No.
• Alloy No. S02 has a composition of Zn-62.9 mass% Cu-0.94 mass% Si-0.082 mass% P-0.067 mass% Pb-0.03 mass% Sn.
• Process No. A14H the molten metal was poured at 1080°C and cast into a sand mold, removed from the sand mold at 650°C, and naturally cooled as it was, with an average cooling rate of 20°C/min in the temperature range from 500°C to 300°C.
• 2B is a cross-sectional metal structure photograph including a portion exhibiting maximum corrosion depth, showing the results of a dezincification corrosion test performed on the alloy casting of FIG. 2A in accordance with the ISO 6509 test method.
• Alloy No. S12 has a composition of Zn-63.6 mass% Cu-1.04 mass% Si-0.070 mass% P-0.062 mass% Pb alloy-0.003 mass% Bi.
• Process No. B1 the molten metal is poured into a mold at 960 ° C., removed from the mold at 750 ° C., and the cooling treatment is started at 560 ° C., and the average cooling rate in the temperature range from 550 ° C. to 500 ° C. is 1020 ° C. / min, and the average cooling rate in the temperature range from 500 ° C.
• 3B is a cross-sectional metal structure photograph including a portion exhibiting maximum corrosion depth, showing the results of a dezincification corrosion test performed on the alloy casting of FIG. 3A in accordance with the ISO 6509 test method.
• 1 is a photograph of the structure of a copper alloy casting according to an embodiment, the copper alloy casting being obtained by subjecting Alloy No. S12 to Process No. B11H.
• Alloy No. S12 has a composition of Zn-63.6 mass% Cu-1.04 mass% Si-0.070 mass% P-0.062 mass% Pb-0.003 mass% Bi.
• 4B is a cross-sectional metal structure photograph including a portion exhibiting maximum corrosion depth, showing the results of a dezincification corrosion test performed on the alloy casting of FIG. 4A in accordance with the ISO 6509 test method.
• 1 is a photograph of the structure of a copper alloy casting according to an embodiment, in which the copper alloy casting was obtained by subjecting Alloy No. S02 to Process No. A14H and Process No. G1. In detail, Alloy No.
• S02 has a composition of Zn-62.9 mass% Cu-0.94 mass% Si-0.082 mass% P-0.067 mass% Pb-0.03 mass% Sn.
• Process No. A14H the molten metal was tapped at 1080°C and cast into a sand mold, removed from the sand mold at 650°C, and naturally cooled as it was, with an average cooling rate of 20°C/min in the temperature range from 500°C to 300°C. Then, Process No. G1 was applied to the obtained casting. In G1, the casting was heated at 580°C for 20 minutes, and the cooling treatment was started at 575°C.
• the average cooling rate in the temperature range from 550°C to 500°C was 1200°C/min
• the average cooling rate in the temperature range from 500°C to 300°C was 1200°C/min.
• 5B is a cross-sectional metal structure photograph including a portion exhibiting maximum corrosion depth, showing the results of a dezincification corrosion test performed on the alloy casting of FIG. 5A in accordance with the ISO 6509 test method.
• a free-cutting copper alloy casting and a method for producing the free-cutting copper alloy casting according to an embodiment of the present invention will be described.
• Applications of the free-cutting copper alloy castings according to the embodiments of the present invention include drinking water and sanitary equipment, musical instruments, tableware, electric, home appliance and electronic device parts, automobile parts, machine parts, stationery, precision machine parts, medical parts, and equipment and parts related to liquids and gases such as industrial water, wastewater and hydrogen.
• Specific part names include water taps, mixer taps, stopcocks, valves, cocks, joints, water meters, gears, sensors, nuts, screws, connectors, etc.
• compositional relations f1, f2, and f0 as follows.
• Compositional formula: f1 [Cu] - 4.8 x [Si] + 0.5 x ([Pb] + [Bi]) - [P].
• the area ratio of the ⁇ phase is represented as ( ⁇ )%, the area ratio of the ⁇ phase as ( ⁇ ), the area ratio of the unmodified ⁇ phase as ( ⁇ ), and the area ratio of the modified ⁇ 1 phase as ( ⁇ 1)%.
• the area ratio of each phase is also referred to as the amount of each phase, the proportion of each phase, or the proportion occupied by each phase.
• a plurality of organization relationship expressions are defined as follows.
• a free-cutting copper alloy casting according to a third embodiment of the present invention contains more than 60.5 mass% and less than 65.0 mass% Cu, more than 0.50 mass% and less than 1.20 mass% Si, 0.002 mass% or more and less than 0.20 mass% Pb, more than 0.01 mass% and less than 0.18 mass% P, and more than 0.05 mass% and less than 0.70 mass% Sn, and any optional elements.
• compositional equations f0, f1, f2, structure-based equations f3, f4 (f4A), f5, structure-compositional equation f6 (f6A), metal structure, etc. as described above.
• Cu is a main element of the free-cutting copper alloy of this embodiment, and in order to overcome the problems of the present invention, it is necessary to contain at least 60.5 mass% or more of Cu.
• the proportion of ⁇ 1 phase exceeds 80%, resulting in low ductility and brittleness.
• the modification of the ⁇ phase is not performed sufficiently, and the dezincification corrosion resistance, stress corrosion cracking resistance, and machinability are deteriorated, resulting in poor ductility.
• the lower limit of the Cu content is more than 60.5 mass%, preferably 61.0 mass% or more, more preferably 61.5 mass% or more, and even more preferably 62.0 mass% or more.
• the Cu content is 65.0 mass% or more, the proportion of the ⁇ 1 phase decreases, depending on the contents of Si, Zn, P, Pb, Bi, and Sn and the manufacturing process. As a result, excellent machinability is not obtained and the strength is also reduced. Therefore, the Cu content is less than 65.0 mass%, preferably 64.8 mass% or less, and more preferably 64.5 mass% or less.
• (Si) Si is a main element of the free-cutting copper alloy of this embodiment, and Si contributes to the formation of metal phases such as ⁇ phase, ⁇ phase, ⁇ phase, ⁇ phase, ⁇ 1 phase, and ⁇ phase.
• the ⁇ phase is modified to form the ⁇ 1 phase.
• the modified ⁇ 1 phase improves machinability and significantly improves the dezincification corrosion resistance and stress corrosion cracking resistance, which were drawbacks of the conventional ⁇ phase.
• a typical composition of the modified ⁇ 1 phase is about 61 mass% Cu, about 1.2 mass% Si, about 37.5 mass% Zn, and about 0.1 mass% P.
• the ⁇ phase has a typical composition of about 66 mass% Cu, about 0.7 mass% Si, and about 33 mass% Zn.
• the inclusion of Si slightly improves the machinability, dezincification corrosion resistance, and stress corrosion cracking resistance of the ⁇ phase, and improves the strength.
• the modified ⁇ 1 phase and the improved ⁇ phase improve the machinability, dezincification corrosion resistance, stress corrosion cracking resistance, and strength of the alloy.
• a certain amount of ⁇ phase is necessary, and for example, if there is no ⁇ phase, the ⁇ phase will not be modified.
• the ⁇ phase In order to improve the dezincification corrosion resistance, stress corrosion cracking resistance, machinability, impact properties, and ductility of the alloy, the ⁇ phase must be 20% or more, preferably 30% or more, in terms of area ratio.
• Si is an essential element for modifying the ⁇ phase, and after solidification, Si dissolves in the ⁇ phase, and the more Si, the more the ⁇ phase is modified, resulting in a ⁇ 1 phase with better properties.
• the inclusion of Si increases the strength of the alloy and improves the flowability during casting.
• the Si content is 0.60 mass% or more, more preferably 0.65 mass% or more, and even more preferably 0.70 mass% or more.
• the amount of Si reaches a certain amount, the modification of the ⁇ 1 phase is saturated.
• the Si content is too high, the conductivity is low, the ductility is poor, and the impact properties are deteriorated. In some cases, the ⁇ phase appears. Meanwhile, in Patent Documents 3 to 9, it is said that the ⁇ phase improves machinability.
• the present application which is mainly composed of the ⁇ 1 phase and the ⁇ phase, the presence of the ⁇ phase rather deteriorates the machinability, reduces the ductility and impact properties of the alloy, and deteriorates the dezincification corrosion resistance and stress corrosion cracking resistance. Therefore, it is preferable to limit the amount of Si and the amount of the ⁇ phase. For these reasons, the amount of Si is less than 1.20 mass%, preferably 1.10 mass% or less. If the electrical conductivity and thermal conductivity are important, the amount of Si is 1.00 mass% or less.
• Zn Zn is a main constituent element of the free-cutting copper alloy of this embodiment, and is an element necessary for improving machinability, strength, high-temperature properties, and castability.
• Zn is the balance, if forced to state, the Zn content is less than about 38.5 mass%, preferably less than 38.0 mass%, and more than about 32.0 mass%, and preferably more than 33.0 mass%.
• P is an essential element for reforming the ⁇ phase to the ⁇ 1 phase. After solidification, P dissolves in the ⁇ phase together with Si, and in the cooling process after solidification, the ⁇ 1 phase is obtained by cooling the casting at a temperature of 500°C and in the temperature range from 500°C to 300°C at a cooling rate of more than 300°C/min.
• the reforming of the ⁇ phase to the ⁇ 1 phase improves machinability and significantly improves the dezincification corrosion resistance and stress corrosion cracking resistance, which were problems with the conventional ⁇ phase.
• compounds of P and Zn or Si reduce cutting resistance and improve chip breakability, but when the cooling process is started at a temperature exceeding about 550°C or about 530°C and cooled at a cooling rate of more than 300°C/min, compounds containing P do not exist or exist in small amounts.
• the effect of modifying the ⁇ phase to the ⁇ 1 phase exceeds the effect of the presence of a compound of the Si-containing ⁇ phase and P, and particularly during high-speed cutting, the effect of modifying to the ⁇ 1 phase is significantly greater.
• the inclusion of P improves the dezincification corrosion resistance of the ⁇ phase, leading to a significant improvement in the dezincification corrosion resistance of the alloy consisting of the ⁇ 1 phase and the ⁇ phase.
• the content of P In order to modify the ⁇ phase to the ⁇ 1 phase, the content of P must be at least 0.01 mass% or more. In order to further modify the ⁇ 1 phase, the amount of P is preferably 0.03 mass% or more, more preferably 0.04 mass% or more, which further improves dezincification corrosion resistance and machinability. In addition, P easily forms compounds with Zn, Si, Mn, Fe, Cr, Co, Al, etc. When P forms compounds with these elements, the amount of P dissolved in the ⁇ phase in the alloy is reduced during the cooling process after solidification, and the reforming to the ⁇ 1 phase is hindered.
• the formation of compounds between Zn and Si, which are the main elements of the alloy of the present application, and P begins at about 550°C, and the amount of P compounds increases as the cooling rate slows.
• the formation of compounds between Mn, Fe, Cr, Co, which are unavoidable impurities, and P begins at about 550°C or a temperature exceeding about 550°C, and the formation of P compounds is further promoted as the amount of these elements increases.
• the presence of Mn, Fe, Cr, and Co hinders the reforming to the ⁇ 1 phase, resulting in an increase in the cutting resistance of the alloy and a deterioration in the dezincification corrosion resistance and stress corrosion cracking resistance. Therefore, the total content of Fe, Mn, Co and Cr must be less than 0.50 mass%, preferably less than 0.35 mass%.
• the formation of P, Zn, and Si compounds has a positive effect on machinability, but the modification of the ⁇ phase to the ⁇ 1 phase and the presence of P, Zn, and Si compounds are fundamentally contradictory.
• the formation of the ⁇ 1 phase requires rapid cooling at 500°C after solidification and in the temperature range from 500°C to 300°C, whereas the sufficient formation of P, Zn, and Si compounds requires slow cooling in the temperature range from about 530°C to about 450°C.
• the modification of the ⁇ phase to the ⁇ 1 phase and the formation of P compounds are in opposite directions, if the cooling rate suddenly increases at the boundary of about 515°C during cooling, for example, P compounds are formed and the ⁇ phase is also modified. However, in that case, the modification of the ⁇ phase is slightly insufficient.
• the P content is less than 0.18 mass%, preferably 0.15 mass% or less, and more preferably 0.12 mass% or less.
• the ⁇ 1 phase containing Si and P provides good machinability as an alloy, but the inclusion of a small amount of Pb further improves the machinability.
• about 0.001 mass% of Pb is dissolved in the matrix, and any excess amount of Pb exists as fine Pb particles with a diameter of about 0.1 to about 2 ⁇ m.
• the inclusion of about 0.1 mass% of Pb hardly contributes to improving the machinability.
• FIG. 6 shows the relationship between the amount of Pb and the machinability when the machinability of a Cu-Zn-Pb alloy containing 62 to 65 mass% of Cu, about 3.2 mass% of Pb, and the balance Zn is taken as 100%. From FIG. 6, it is shown that the content of 0.1 mass% Pb has only an effect of improving the machinability by only about 5%, from about 25% to about 30% in the machinability index. On the other hand, in the present application, even a small amount of Pb has a great effect on the machinability, and the effect is exhibited at a content of 0.002 mass% or more.
• the Pb content is preferably 0.003 mass% or more, and more preferably 0.01 mass% or more.
• the Pb content is preferably 0.03 mass% or more, and the machinability of the alloy is greatly improved by the ⁇ 1 phase with greatly improved machinability and the inclusion of a small amount of Pb. It is well known that Pb improves the machinability of copper alloys, and for this purpose, about 3 mass% of Pb is required in a binary alloy of Cu-Zn, as typified by free-cutting brass bar C3604.
• an alloy with excellent machinability is completed by having a ⁇ 1 phase containing Si and P and a small amount of Pb particles, or Pb and Bi particles described later, present in the metal structure.
• the upper limit of Pb is set to less than 0.20 mass%.
• the content of Pb is preferably less than 0.10 mass%, and is optimally 0.08 mass% or less in consideration of the effects on the human body and the environment.
• Bi Like Pb, Bi is dissolved in the matrix in an amount of about 0.0001 mass%, and any Bi in excess of this amount exists as particles with a diameter of about 0.1 to about 2 ⁇ m. When both Pb and Bi are added, most of the Bi and Pb are mixed and exist as particles with a diameter of about 0.1 to about 2 ⁇ m. In this embodiment, it was found that by including Bi together with Pb in the presence of the ⁇ 1 phase, machinability equivalent to or greater than that obtained when Pb and Bi are each contained alone can be obtained. The function of improving machinability by Bi was considered to be inferior to that of Pb, but in this embodiment, it was found that it exhibits the same effect as Pb, and in some cases, even exceeds that of Pb. Incidentally, Bi deteriorates the stress corrosion cracking resistance of brass, but when it exists as a particle in which Pb and Bi are mixed, or when the amount of Bi is small, there is almost no effect on stress corrosion cracking.
• Bi When Bi is contained, at least 0.0001 mass% or more of Bi is required in order to have good machinability as an alloy with a small amount of Pb contained.
• the amount of Bi is preferably 0.001 mass% or more, and more preferably 0.002 mass% or more.
• the amount of Bi is less than 0.20 mass%, preferably less than 0.10 mass%, and more preferably 0.08 mass% or less.
• the amount is set as described above, there is no risk of cracking during casting.
• the total content of Pb and Bi is set to less than 0.20 mass%, preferably less than 0.10 mass%.
• Sn Sn is dissolved in the ⁇ 1 phase, which further improves the dezincification corrosion resistance of the ⁇ 1 phase and improves the dezincification corrosion resistance of the alloy.
• Sn When Sn is contained, in order to obtain this effect, Sn needs to be contained in an amount exceeding 0.05 mass%, preferably 0.10 mass% or more.
• Sn is originally distributed more in the ⁇ phase and ⁇ 1 phase than in the ⁇ phase, and a small amount of Sn improves the dezincification corrosion resistance, but when the Sn concentration is high, the ⁇ phase is easily formed and the ductility is reduced.
• the formation of the ⁇ phase not only leads to a decrease in ductility as an alloy, but also reduces machinability and deteriorates the dezincification corrosion resistance.
• the content of Sn needs to be kept at least less than 0.70 mass%, preferably less than 0.60 mass%, and more preferably 0.50 mass% or less.
• Sn is distributed in large amounts in the ⁇ and ⁇ 1 phases, and it has been found that a high Sn content can cause problems in modifying the ⁇ phase, which contains Si and P. Specifically, it has been found that when the amount of Sn is greater than the amount of Si, the modification of the ⁇ phase becomes insufficient, and the effect of the Sn content in improving dezincification corrosion resistance is offset. As will be described later, the amount of Si must exceed the amount of Sn.
• inevitable impurities include Mn, Fe, Al, Ni, Mg, Se, Te, Sn, Bi, Co, Ca, Zr, Cr, Ti, In, W, Mo, B, Ag, and rare earth elements.
• free-cutting copper alloys particularly free-cutting brass containing Zn at about 30 mass% or more, are not primarily made from high-quality raw materials such as electrolytic copper and electrolytic zinc, but from recycled copper alloys.
• downstream processes downstream processes, processing processes
• most members and parts are cut, generating a large amount of discarded copper alloy at a ratio of 40 to 80 parts by mass per 100 parts by mass of material.
• Examples include cutting chips, scraps, burrs, runners, products with manufacturing defects, and discarded products. These discarded copper alloys are the main raw materials. If the separation of cutting chips and scraps is insufficient, Pb, Fe, Mn, Si, Se, Te, Sn, P, Sb, As, Bi, Ca, Al, Zr, Ni and rare earth elements are mixed in as raw materials from free-cutting brass with Pb added, free-cutting copper alloys that do not contain Pb but contain Bi, special brass alloys that contain Si, Mn, Fe and Al, and other copper alloys. Cutting chips also contain Fe, W, Co, Mo, etc., which are mixed in from tools. Recycled waste products contain plated products, so Ni, Cr and Sn are mixed in. Pure copper scrap used instead of electrolytic copper contains Mg, Sn, Fe, Cr, Ti, Co, In, Ni, Se and Te. Brass-based scrap used in place of electrolytic copper and electrolytic zinc is often plated with Sn, resulting in Sn contamination.
• scrap containing these elements is used as a raw material, at least to the extent that it does not adversely affect the properties.
• the essential element Pb is contained in an amount of about 3 mass%, and further, as impurities, Fe is allowed to be 0.5 mass%, and Fe + Sn (the total amount of Fe and Sn) is allowed to be up to 1.0 mass%.
• the essential element Pb is contained in an amount of about 2 mass%, and the allowable limits of the remaining components are 0.8 mass% Fe, 1.0 mass% Sn, 0.5 mass% Al, and 1.0 mass% Ni.
• high concentrations of Fe, Sn, Al, and Ni close to the upper limits of the JIS standard are sometimes contained in free-cutting brass rods and brass castings.
• Fe, Mn, Co, and Cr dissolve in the ⁇ and ⁇ phases of Cu-Zn alloys to a certain concentration, but if Si or P is present, they tend to combine with the Si and P, posing the risk of consuming the Si and P needed to modify the ⁇ phase.
• Si When combined with Si, Fe, Mn, Co, and Cr form Fe-Si compounds, Mn-Si compounds, Co-Si compounds, and Cr-Si compounds in the metal structure.
• P Fe, Mn, Co, and Cr form Fe-P compounds, Mn-P compounds, Co-P compounds, and Cr-P compounds in the metal structure.
• These intermetallic compounds are very hard, so they not only increase cutting resistance, but also shorten the tool life.
• the amounts of Fe, Mn, Co, and Cr must be limited, and each content must be less than 0.35 mass%, preferably less than 0.25 mass%, and more preferably 0.15 mass% or less.
• the total content of Fe, Mn, Co, and Cr must be less than 0.50 mass%, preferably less than 0.35 mass%, more preferably less than 0.30 mass%, and even more preferably 0.25 mass% or less.
• the Al content which is mixed in from special brass rods, brass castings, etc., must be limited because a high content affects the modification and properties of the ⁇ phase. Also, Al forms compounds with P or Si. In the alloy of this embodiment, the Al content must be less than 0.30 mass%, more preferably less than 0.15 mass%, and even more preferably 0.10 mass% or less.
• Ni is often mixed in from scraps, etc. Although Ni has a relatively small effect on mechanical properties such as machinability, it is necessary to limit it in consideration of its effect on the human body.
• the Ni content is preferably less than 0.20 mass%, more preferably less than 0.10 mass%.
• Ag is generally regarded as Cu and has almost no effect on various properties, so there is no need to particularly limit it, but the Ag content is preferably less than 0.05 mass%.
• Te and Se are elements themselves that have free machinability, and although rare, there is a risk of being mixed in large amounts.
• the respective contents of Te and Se are preferably less than 0.10 mass%, more preferably less than 0.05 mass%, and even more preferably 0.02 mass% or less.
• corrosion-resistant brass contains As and Sb to improve the corrosion resistance of brass.
• the content of each of As and Sb is preferably less than 0.05 mass%, and more preferably 0.02 mass% or less.
• the content of each of the other elements, such as Mg, Ca, Zr, Ti, In, W, Mo, B, and rare earth elements, is preferably less than 0.05 mass%, more preferably less than 0.03 mass%, and further preferably 0.02 mass% or less.
• the content of rare earth elements is the total amount of one or more of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, and Lu.
• the total amount of inevitable impurities other than Fe, Mn, Co, Cr and Al is preferably less than 0.70 mass%, and more preferably less than 0.50 mass%.
• compositional formula f1 [Cu] - 4.8 x [Si] + 0.5 x ([Pb] + [Bi]) - [P] - [Sn].
• Sn content is 0.05 mass% or less
• [Sn] in f1 is 0, and when Bi is not contained, [Bi] in f1 is 0.
• Sn is 0.05 mass% or less, the effect on compositional formula f1 is small, so it is not specified in compositional formula f1.
• the compositional relational formula f1 is a formula that expresses the relationship between the composition and the metal structure.
• the various characteristics targeted by this embodiment cannot be satisfied. If the compositional formula f1 is less than 57.3, the proportion of the ⁇ phase and the ⁇ 1 phase increases, the modification of the ⁇ phase becomes insufficient, and the dezincification corrosion resistance, stress corrosion cracking resistance, ductility, and impact properties become poor. Therefore, the lower limit of the compositional formula f1 is 57.3 or more, preferably 58.0 or more, and more preferably 58.5 or more.
• the proportion of the ⁇ phase increases, the modification of the ⁇ phase becomes sufficient, and excellent machinability is maintained while good dezincification corrosion resistance is provided, and good ductility and impact properties are obtained.
• the upper limit of the compositional relational formula f1 affects the proportion of the ⁇ phase and ⁇ 1 phase, and when the compositional relational formula f1 is greater than 60.8, the proportion of the ⁇ phase and ⁇ 1 phase decreases. As a result, excellent machinability cannot be obtained and the strength is also reduced.
• the upper limit of f1 is also related to castability.
• the upper limit of the compositional relational formula f1 is 60.8 or less, preferably 60.5 or less, and more preferably 60.1 or less.
• the value of the compositional relational formula f1 decreases, the amount of the ⁇ 1 phase increases, the machinability improves, the strength increases, the solidification temperature range decreases, and the castability improves.
• compositional formula f0 Sn is contained to further improve the dezincification corrosion resistance.
• Sn is contained in a large amount in the ⁇ phase, and the greater the amount of Sn, the more the dezincification corrosion of the ⁇ 1 phase is delayed.
• the amount of Sn is greater than the amount of Si, it may hinder the modification of the ⁇ phase, and may impair the dezincification corrosion resistance and machinability.
• the free-cutting copper alloy casting according to this embodiment has good dezincification corrosion resistance and stress corrosion cracking resistance while containing a large amount of ⁇ phase, whereas in this application, ⁇ 1 phase is used in the conventional case. It also has machinability, which requires a kind of brittleness that reduces the resistance during cutting and breaks the chips into small pieces, and ductility and impact properties, which are completely contradictory properties.
• Tables 1 to 4 show the results of comparing the compositions of the Cu-Zn-Si alloys and the like described in the above-mentioned Patent Documents 1 to 16 with the alloy of this embodiment.
• Patent Document 9 differ in the contents of the main elements Si and Cu
• the present embodiment and Patent Document 10 differ in the content of the main element Si
• the present embodiment and Patent Document 16 differ in the content of the main element Cu.
• Patent Documents 1 and 2 do not contain Si.
• Patent Documents 2, 14, and 16 state that Pb is not contained, and the Pb content is different.
• Patent Documents 9, 11, 12, and 13 the ⁇ phase in the metal structure is significantly restricted from the viewpoints of machinability, dezincification corrosion resistance, corrosion resistance, etc. Although the ⁇ 1 phase and the ⁇ phase are completely different, Patent Documents 9, 11, 12, and 13 respectively restrict the ⁇ phase to 5% or less, 25% or less, 15% or less, and 0.9% or less.
• Patent Document 11 relates to a near-net-shape tubular hot forged product, and uses a tubular material.
• heat treatment is performed at a temperature of 350 to 550° C. or 400 to 600° C. in order to reduce the ⁇ phase and to break up the ⁇ phase.
• the steel contains 0.2 mass% or more of Sn, contains Sn and Si to improve the dezincification corrosion resistance of the ⁇ phase, and requires hot extrusion at a temperature of 700° C. or more to improve machinability and heat treatment at 400 to 600° C. to improve corrosion resistance.
• the proportion of the ⁇ phase is approximately 5 to 20%, and the content of Si is 0.1 to 0.4 mass%, and may be controlled to 0.2 mass% or less.
• Patent Documents 13, 14, and 15 Al is considered to be essential for improving discoloration resistance, castability, and dezincification corrosion resistance.
• Patent Document 15 in order to improve dezincification corrosion resistance, Sn and Al are contained in an amount of at least 0.1 mass% each, and in order to obtain excellent machinability, it is necessary to contain large amounts of Pb and Bi.
• Patent Document 16 a corrosion-resistant copper alloy casting having good mechanical properties and castability is obtained by not including Pb, but requiring a ⁇ phase, and by including 65 mass% or more of Cu and Si, as well as trace amounts of Al, Sb, Sn, Mn, Ni, B, etc.
• Patent documents 3 to 8 all require that, during the cooling process after casting and solidification or hot working, a treatment is carried out so that the average cooling rate in the temperature range from about 530°C to about 450°C is about 0.1°C/min to about 70°C/min, and that the resulting P compounds are present in the metal structure.
• the ⁇ phase is effective for machinability, and do not mention the modification of the ⁇ phase at all, and are silent about dezincification corrosion resistance and stress corrosion cracking resistance, and no data is disclosed.
• no data is disclosed regarding cutting resistance under high-speed cutting conditions.
• cooling is performed at a cooling rate of more than 300°C/min, and preferably the cooling process is started at a temperature lower than 700°C and higher than 500°C, and the average cooling rate from 500°C to 300°C exceeds 300°C/min, which is basically the opposite of Patent documents 3 to 8.
• compounds of P and Zn or Si may be present, but the amount of P compounds, if any, is small.
• Patent Documents 3 to 8 there is no mention whatsoever of the ⁇ phase being modified or the modified ⁇ phase, i.e., the ⁇ 1 phase.
• the ⁇ phase with Si and P dissolved therein is modified to the ⁇ 1 phase by cooling at a cooling rate of more than 300°C/min at 500°C and by cooling at an average cooling rate of at least 300°C/min in the temperature range from 500°C to 300°C. If the average cooling rate is from about 0.1°C/min to about 70°C/min in the temperature range from about 530°C to about 450°C, the ⁇ phase is not modified.
• Patent documents 3 to 8 disclose metal structures etched with a mixture of hydrogen peroxide and aqueous ammonia, but in none of them are grain boundaries observed within the ⁇ phase.
• Beta1 phase differs from conventional beta phase in that it significantly improves dezincification corrosion resistance and stress corrosion cracking resistance. It also further improves machinability, with the presence of the beta1 phase exceeding the machinability achieved when a beta phase containing Si and a P compound are present. However, to achieve this, the beta1 phase must be present in an area ratio of more than 25% in the metal structure. In addition, while the present application states that the presence of a gamma phase impairs machinability, Patent Documents 3 to 8 state that the gamma phase is effective in improving machinability.
• the metal structure of the present application is composed of ⁇ phase, ⁇ 1 phase, and in some cases, a small amount or 0% of ⁇ phase.
• the metal structure is only the above-mentioned constituent phases.
• the metal structure may contain precipitates such as compounds containing P and compounds containing Si, crystallized substances, Pb or Bi particles, oxides, sulfides, and inclusions. In the case of castings, oxides and crystallized substances are often contained in larger amounts than hot extrusion materials.
• the ⁇ phase and ⁇ 1 phase are easily distinguishable.
• a grain boundary pattern i.e., grain boundaries
• the ⁇ 1 phase is etched with a mixture of hydrogen peroxide and ammonia water, and the ⁇ phase is converted to the ⁇ 1 phase
• a grain boundary pattern i.e., grain boundaries
• the ⁇ 1 phase is obtained by maintaining the ⁇ phase, in which a certain amount of Si and P are dissolved, at a high temperature of over 500°C after solidification, i.e., at about 500-700°C, and then cooling from that temperature range (cooling at a cooling rate at 500°C and an average cooling rate from 500°C to 300°C exceeding at least 300°C/min, and continuing to cool to near room temperature) to bring the metal structure state at 500-700°C to room temperature.
• the cooling rate is increased in the temperature range from the cooling treatment start temperature of 500-700°C to 300°C, and the material is rapidly cooled to room temperature of 100°C or less. This brings the metal structure state at 500-700°C to room temperature.
• the ⁇ 1 phase is obtained. If a similar cooling treatment is performed on the ⁇ phase of a Cu-Zn alloy that does not contain both the specified amounts of Si and P, the ⁇ 1 phase cannot be obtained. Similarly, when an alloy containing a predetermined amount of Si and P is cooled at a cooling rate of 300°C/min or less at 500°C, the ⁇ 1 phase is not obtained. When the temperature range from 500°C to 300°C is cooled at an average cooling rate of 300°C/min or less, the ⁇ 1 phase is not obtained. When the cooling treatment is performed at a temperature lower than 500°C, for example, from 450°C, the ⁇ 1 phase is not obtained.
• a predetermined amount of ⁇ phase is required to modify the ⁇ phase, and if the ⁇ phase is small, the ⁇ phase is not modified and the ⁇ 1 phase is not obtained.
• the degree of modification of the ⁇ phase is also affected by the amount of Si, P, the amount of unavoidable impurities such as Fe and Al, the cooling rate at 500°C, the average cooling rate from 500°C to 300°C, and the cooling treatment start temperature.
• the degree of modification of the ⁇ phase begins to roughly saturate at approximately 1 mass% Si and 0.1 mass% P, and if these amounts are too high, this can cause problems such as poor thermal and electrical conductivity, ductility, and the appearance of the ⁇ phase.
• the modified ⁇ 1 phase can overcome the drawbacks of the ⁇ phase of Cu-Zn alloys, and the major issues of the alloy's dezincification corrosion resistance and stress corrosion cracking resistance. That is, as an example, in concrete figures, the corrosion progress of dezincification corrosion can be delayed to about 1/2 or 1/2 or less.
• dezincification corrosion of Cu-Zn alloys containing a ⁇ phase is a major problem, and since dezincification corrosion occurs first along the ⁇ phase, the amount of the ⁇ phase is limited to 25% or less or 20% or less, and in order to further reduce the amount of the ⁇ phase and to divide the ⁇ phase, a heat treatment at 350 to 550 ° C. is performed.
• the ⁇ 1 phase In the Cu-Zn-Si-P-Pb alloy, which is the free-cutting copper alloy of this embodiment, in order to obtain good machinability while minimizing the Pb content, at least the ⁇ 1 phase needs to have an area ratio of more than 25%. Furthermore, in order to improve machinability and strength, the ⁇ 1 phase is preferably 30% or more, more preferably 33% or more. On the other hand, if the ⁇ 1 phase is too much, for example 95%, the ⁇ phase is not modified. Since the ⁇ phase is modified in the presence of the ⁇ phase, a certain amount of the ⁇ phase is necessary.
• the ⁇ 1 phase significantly slows down the progress of dezincification corrosion and stress corrosion cracking compared to the ⁇ phase, it is still inferior to the ⁇ phase in dezincification corrosion resistance and stress corrosion cracking resistance.
• the ⁇ phase is selectively dezincified first, and the dezincification corrosion progresses, and the dezincification corrosion depth finally reaches about 500 to 550 ⁇ m.
• the ⁇ 1 phase is selectively dezincified, but the dezincification corrosion depth is about 20 to 240 ⁇ m, and the progress of dezincification corrosion is significantly suppressed compared to when the metal structure is composed of ⁇ and ⁇ phases.
• the ⁇ phase is reformed to the ⁇ 1 phase, and the dezincification corrosion resistance is significantly improved, but the dezincification corrosion resistance and impact properties are inferior to those of the ⁇ phase, so if the area ratio of the ⁇ 1 phase is high, the dezincification corrosion resistance and impact properties of the alloy are deteriorated.
• the area ratio of the ⁇ 1 phase needs to be set to 80% or less, preferably 70% or less, and more preferably 65% or less.
• the unmodified ⁇ phase is distinguished as having the structural formula f4A.
• the metal structure of the present application is basically composed of ⁇ phase and ⁇ 1 phase, and a cooling treatment is carried out to reform the ⁇ phase into the ⁇ 1 phase, but the ⁇ phase is hardly affected by the cooling treatment.
• a certain amount of ⁇ phase is necessary to reform the ⁇ phase. If there is too much ⁇ 1 phase, the ductility and impact properties of the alloy will be problematic, and an appropriate amount of ductile ⁇ phase is necessary. Conversely, if there is too much ⁇ phase, the strength will be low.
• the ⁇ phase containing Si only improves machinability slightly compared to the ⁇ phase not containing Si, and the amount of ⁇ phase is limited, especially from the viewpoint of machinability.
• the soft ⁇ phase plays the role of a cushioning material during cutting, or plays the role of a stress concentration source at the boundary with the hard ⁇ 1 phase during cutting, and even if the alloy contains up to about 75% of the ⁇ phase, the cutting resistance of the alloy is maintained low and the chips are broken.
• the ⁇ phase plays the role of a cushioning material during cutting and also plays the role of a stress concentration source at the boundary with the ⁇ 1 phase, it is preferable that the ⁇ phase be fine and in a granular shape.
• the amount of the ⁇ phase must be 20% or more, preferably 30% or more, and more preferably 35% or more.
• the upper limit of the ⁇ phase is less than 75%, preferably 70% or less, and more preferably 67% or less.
• the ⁇ phase is a phase that contributes to machinability in Cu-Zn-Si alloys having a Cu concentration of about 69-80 mass% and a Si concentration of about 2-4 mass%.
• Patent Document 16 states that the ⁇ phase is essential in Pb-free Cu-Zn-Si alloys, and Patent Documents 3-7 also state that the Si-containing ⁇ phase has good machinability, and that the Si-containing ⁇ phase also contributes to machinability.
• the gamma phase is considered to hinder the machinability of the alloy, and is therefore given a negative coefficient greater than the coefficient of the amount of the beta phase in the structure-composition relational expression f6 described below.
• the gamma phase impairs the impact properties and deteriorates the dezincification corrosion resistance. This is because, in this embodiment, the beta phase is modified but the gamma phase is not modified.
• the structure-composition relational formula f6 is a simple conditional formula for obtaining good machinability as an alloy.
• the amount of ⁇ 1 phase, the amount of Si contained in the alloy within the composition range of the present application, the amount of Pb and Bi, and the amount of P are arranged as positive effects, and the amount of ⁇ phase is arranged as negative effects.
• the ⁇ 1 phase containing Si and P is obtained by multiplying the amount of ⁇ 1 phase by (-0.5 x [Si] 2 + 1.5 x [Si]), multiplying the sum of the amounts of Pb and Bi to the 1/2 power by a coefficient of 25, multiplying the amount of P to the 1/2 power by a coefficient of 12, and subtracting the sum of these by multiplying the amount of ⁇ phase by a coefficient of 2.
• the performance of the ⁇ 1 phase is directly affected by the Si concentration, which is in turn affected by the P concentration. Furthermore, the inclusion of a very small amount of Pb or Bi improves machinability. On the other hand, in this application, the ⁇ phase impairs machinability. It has been discovered that the degree of improvement in machinability due to Pb or Bi is closely related to the 1/2 power of the amount of Pb and Bi. A very small amount of Pb or Bi has a significant effect, and as the content increases, the effect of improving machinability increases, but the effect becomes gradually more gradual.
• the structure-composition relationship f6 should be greater than 28, preferably greater than 35, and more preferably greater than 40, approaching the machinability of a free-cutting brass bar containing 3 mass% Pb.
• the machinability is highest when the structure-composition relationship f6 value is about 55 to 80, and as the value of f6 increases further, the machinability actually decreases. This is because the effect of the amount of ⁇ 1 phase on machinability saturates at about 60%, and the effect of Si on machinability saturates at roughly 1 mass%.
• the amount of ⁇ phase f4A ( ⁇ phase) was added to the amount of ⁇ 1 phase f4 ( ⁇ 1 phase), and applied to the formula for f6 to calculate a reference value, f6A.
• 1A to 5B show photographs of the metal structures of various alloy castings and photographs of the results of the ISO6509 dezincification corrosion test.
• 1A is a photograph of the structure of a copper alloy casting in an embodiment, and the copper alloy casting was obtained by subjecting Alloy No. S02 to Process No. A1.
• Alloy No. S02 has a composition of Zn-62.9 mass% Cu-0.94 mass% Si-0.082 mass% P-0.067 mass% Pb-0.03 mass% Sn.
• FIG. 1B is a cross-sectional metal structure photograph including a portion exhibiting the maximum corrosion depth, showing the results of a dezincification corrosion test performed on the alloy casting of FIG. 1A in accordance with the ISO 6509 test method.
• FIG. 2A is a photograph of the structure of a copper alloy casting in an embodiment, and the copper alloy casting was obtained by subjecting Alloy No. S02 to Process No. A14H.
• Alloy No. S02 has a composition of Zn-62.9 mass% Cu-0.94 mass% Si-0.082 mass% P-0.067 mass% Pb-0.03 mass% Sn.
• Process No. A14H the molten metal was poured at 1080°C and cast into a sand mold, removed from the sand mold at 650°C, and naturally cooled as it was, and the average cooling rate in the temperature range from 500°C to 300°C was 20°C/min.
• FIG. 2B is a cross-sectional metal structure photograph including a portion exhibiting the maximum corrosion depth, showing the results of a dezincification corrosion test performed on the alloy casting of FIG. 2A in accordance with the ISO 6509 test method.
• Alloy No. S12 has a composition of Zn-63.6 mass% Cu-1.04 mass% Si-0.070 mass% P-0.062 mass% Pb alloy-0.003 mass% Bi.
• Process No. B1 the molten metal is poured into a mold at 960 ° C., removed from the mold at 750 ° C., and the cooling process is started at 560 ° C., the average cooling rate in the temperature range from 550 ° C. to 500 ° C. is 1020 ° C. / min, and the average cooling rate in the temperature range from 500 ° C.
• FIG. 3B is a cross-sectional metal structure photograph including a portion exhibiting the maximum corrosion depth, showing the results of a dezincification corrosion test performed on the alloy casting of FIG. 3A in accordance with the ISO 6509 test method.
• 4A is a photograph of the structure of a copper alloy casting in an embodiment, and the copper alloy casting was obtained by subjecting Alloy No. S12 to Process No. B11H.
• Alloy No. S12 has a composition of Zn-63.6 mass% Cu-1.04 mass% Si-0.070 mass% P-0.062 mass% Pb-0.003 mass% Bi.
• FIG. 4B is a cross-sectional metal structure photograph including a portion exhibiting the maximum corrosion depth, showing the results of a dezincification corrosion test performed on the alloy casting of FIG. 4A in accordance with the ISO 6509 test method.
• Alloy No. S02 has a composition of Zn-62.9 mass% Cu-0.94 mass% Si-0.082 mass% P-0.067 mass% Pb-0.03 mass% Sn.
• Process No. A14H the molten metal was poured at 1080°C and cast into a sand mold, removed from the sand mold at 650°C, and naturally cooled as it was, with an average cooling rate of 20°C/min in the temperature range from 500°C to 300°C. Then, Process No. G1 was applied to the obtained casting.
• FIG. 5B is a cross-sectional metal structure photograph including a portion exhibiting the maximum corrosion depth, showing the results of a dezincification corrosion test performed on the alloy casting of FIG. 5A in accordance with the ISO 6509 test method.
• the grain boundary patterns are clearly recognized in the ⁇ 1 phase in the sand castings, metal mold castings, and castings that were heat-treated from sand castings, and the grain boundaries are observed.
• the grain boundaries refer to the linear patterns that penetrate the ⁇ 1 phase grains observed in the ⁇ 1 phase, as shown in Figure 1A.
• Figures 2A and 4A no grain boundary-like patterns are observed in the ⁇ phase, and the difference between the two is clear. Instead, in Figures 2A and 4A, many fine black granular precipitates are observed, mainly in the ⁇ phase and at the phase boundaries between the ⁇ phase and the ⁇ phase. Conversely, in Figures 1A, 3A, and 5A, only a few black granular precipitates are observed.
• the black granular precipitates of about 0.5 to 3 ⁇ m in size observed in Figures 2A and 4A are present in large numbers mainly in the ⁇ phase and at the phase boundary between the ⁇ phase and the ⁇ phase.
• the granular precipitates are mainly compounds of P with either Zn and/or Si, so-called P compounds.
• some of the precipitates contain inclusions such as Pb particles, mixed particles of Pb and Bi, compounds of Fe, Mn, etc. with P or Si, compounds of Al with P or Si, and oxides. These compounds and inclusions can be identified by microscopic observation, but it is a little difficult to distinguish them in printed photographs. In Figures 2A and 4A, there are about 300 or more P compounds in the field of view of the printed photographs.
• fine granular P compounds are not present or are present only in small amounts, at least 1/10 less than the number of compounds in Figures 2A and 4A. Whether or not grain boundaries exist in the ⁇ 1 phase or ⁇ phase from the cooling history of each sample, and whether or not there are many P compounds, depends on whether the cooling rate at the time when the temperature of the casting is 500°C, i.e., in the temperature range just above 500°C, and the average cooling rate from 500°C to 300°C is faster or slower than 300°C/min.
• the cooling rate at the time when the temperature of the casting is 500°C, i.e., in the temperature range just above 500°C is the average cooling rate from 550°C to 500°C. If the cooling treatment start temperature is lower than 550°C, the average cooling rate from the cooling treatment start temperature to 500°C is used.
• Figures 1B, 2B, 3B, 4B, and 5B The results of the ISO 6509 dezincification corrosion test for these alloys are shown in Figures 1B, 2B, 3B, 4B, and 5B.
• the magnifications of Figures 1B, 3B, and 5B are twice those of Figures 2B and 4B.
• the maximum corrosion depths of the samples in which grain boundaries were observed in the ⁇ 1 phase were all 110 ⁇ m or less ( Figures 1B, 3B, and 5B), but the maximum corrosion depths of the samples in which grain boundaries were not observed in the ⁇ phase ( Figures 2A and 4A) were 480 ⁇ m and 420 ⁇ m ( Figures 2B and 4B), a difference of more than three times the corrosion depth.
• the form of dezincification corrosion was selective corrosion of the ⁇ 1 and ⁇ phases in all cases. Even in the case of a modified ⁇ 1 phase, the ⁇ 1 phase is preferentially corroded by dezincification, just like the ⁇ phase, but the progress of dezincification corrosion of the ⁇ 1 phase can be delayed to at least about 1/2, and even to about 1/3 or less, compared to the ⁇ phase.
• thinner and lighter materials and parts such as drinking water equipment, which are the subject of use in this embodiment.
• thinner materials and lighter weight can be achieved by providing good corrosion resistance and high strength to the materials used.
• castings can have component segregation and microscopic defects, and are not often used for parts that are subjected to cold processing such as crimping or for parts that require ductility during use.
• hardness (Vickers hardness, Rockwell hardness) is used as a method for evaluating strength in accordance with the nature of the castings, and impact test values (U-notch) are used to evaluate toughness and ductility.
• the Vickers hardness is at least 100 Hv and the Rockwell B scale hardness is at least 52. More preferably, the Vickers hardness is at least 110 Hv and the Rockwell B scale hardness is at least 60.
• a Vickers hardness of 100 Hv corresponds to a tensile strength of approximately 400 N/ mm2 and a yield strength of approximately 120 N/ mm2 .
• a brass casting CAC203 containing 1 to 2 mass% Pb has a Vickers hardness of approximately 75 Hv, a Rockwell B scale hardness of approximately 30, a tensile strength of approximately 350 N/ mm2 and a yield strength of approximately 80 N/ mm2 .
• the Charpy impact test value is preferably 25 J/ cm2 or more, more preferably 30 J/ cm2 or more.
• the Charpy impact test value exceeds about 70 J/ cm2 , for example, the so-called stickiness of the material increases, so that the cutting resistance increases and the machinability deteriorates, such as chips tending to form continuous chips.
• the applications of this embodiment include electrical and home appliance parts, automobile parts, etc., and are also substitutes for brass casting CAC203 and bronze casting CAC406 to which Pb is added.
• phosphor bronze JIS standard, C5191, C5210 containing 6 mass% or 8 mass% Sn in the amount of drawn copper products is widely used, and the electrical conductivity of these is about 14% IACS and about 12% IACS, respectively, and the electrical conductivity of CAC203 and CAC406 is about 24% IACS and about 15% IACS, respectively. Therefore, as long as the electrical conductivity of the copper alloy of this embodiment is 15% IACS or more, no problem occurs with respect to electrical conductivity.
• the upper limit of electrical conductivity is not particularly specified because the improved conductivity hardly causes any practical problems.
• the basic premise of the free-cutting copper alloy casting of this embodiment is that a sound casting can be obtained.
• the inclusion of Si suppresses Zn vapor during melting, and good melting and casting can be performed.
• the inclusion of Si and the restrictions of Cu, Zn and f1 provide good melt flow, the molten metal reaches even thin-walled parts, and complex shapes can be cast, and casting defects such as porous shrinkage cavities are unlikely to occur.
• the casting must be free of cracks.
• the first point is whether or not a low-melting point metal exists as a melt at high temperatures after solidification.
• a low-melting point metal exists, it is determined by its amount and whether or not the matrix has ductility at high temperatures.
• the amount of low melting point metals Pb and Bi present in the molten state in the matrix during the solidification and cooling process of the casting is significantly limited to less than 0.20 mass% in total, which is unlikely to lead to casting cracks.
• the ⁇ 1 phase which has excellent ductility at high temperatures, is contained in a large amount, which can cover the adverse effects of the low melting point metal contained in a small amount, and there is no problem with cracking of the casting.
• the metal structure of the free-cutting copper alloy casting of this embodiment varies not only with the composition but also with the manufacturing process.
• There are various casting methods for manufacturing castings such as metal mold, sand mold, continuous casting, die casting, and lost wax casting, and the cooling rate of the casting after solidification is roughly determined by the thickness and shape of the casting, and the material and thickness of the metal mold or sand mold.
• the cooling rate can be changed by cooling methods such as heat retention, water cooling, oil cooling, and forced air cooling. Meanwhile, various changes in the metal structure occur during the cooling process after solidification, and the metal structure changes significantly depending on the cooling rate.
• the change in the metal structure indicates that the type of constituent phases and the amount (area ratio) of these constituent phases change significantly.
• the cooling rate at 500°C and the average cooling rate in the temperature range from 500°C to 300°C are the most important factors during the cooling process, and greatly affect the dezincification corrosion resistance and machinability.
• melting is performed at about 950 to 1200°C, which is about 100 to 300°C higher than the melting point (liquidus temperature) of the alloy of this embodiment.
• the molten metal at about 900 to 1150°C, which is about 50 to 250°C higher than the melting point, is cast into a predetermined mold such as a metal mold, sand mold, or mold, and cooled. After solidification, the constituent phases change in various ways.
• the cooling rate after casting and after solidification varies depending on the weight, thickness, and thermal conductivity of the cast copper alloy, and the material of the casting mold such as sand mold or metal mold.
• a conventional copper alloy casting is cast into a mold made of copper alloy or iron, that is, in the case of mold casting, the casting is removed from the mold at a temperature of about 750° C. or lower after casting, and is air-cooled or slowly cooled at an average cooling rate of about 10 to 200° C./min in the temperature range from 500° C. to 300° C.
• cooling is carried out in roughly the same manner as in metal mold casting, and the cast rod emerging from the iron mold is generally air-cooled, with the cooling rate being determined primarily by the cross-sectional area of the continuously cast rod and the casting speed.
• a continuously cast rod with a diameter of 20 mm it is cooled in the temperature range of 500°C to 300°C at an average cooling rate of about 40 to 100°C/min.
• the copper alloy cast into the sand mold is cooled in the temperature range of 500°C to 300°C at an average cooling rate of about 0.6 to 60°C/min, depending on the size of the casting and the material and size of the sand mold, and when the temperature drops to about 300°C or lower than about 250°C, the casting is removed from the sand mold and air-cooled, or the casting is left in the sand mold until it reaches near room temperature.
• the cooling rate of these castings at 500°C is roughly the same as or slightly faster than the average cooling rate in the temperature range of 500°C to 300°C.
• the metal structure is a single ⁇ phase.
• Subsequent cooling forms various phases such as ⁇ phase and ⁇ phase.
• the cooling rate exceeds 300°C/min when the temperature of the casting is 500°C, and the average cooling rate from 500°C to 300°C is adjusted to exceed 300°C/min, thereby reforming the ⁇ phase to ⁇ 1 phase.
• the cooling process continues even at temperatures lower than 300°C.
• the cooling rate at 500°C is the average cooling rate from the cooling process start temperature to 500°C.
• a preferred cooling method is to start the cooling treatment in the temperature range of 700° C. to 500° C. during the cooling process after solidification.
• the average cooling rate from the cooling treatment start temperature to 500° C. is roughly the same as the average cooling rate from 500° C. to 300° C., and after the temperature of the casting reaches 300° C., the cooling treatment is continued even at temperatures lower than 300° C., and the average cooling rate is slightly slower than that from 500° C. to 300° C., but is roughly the same.
• the ⁇ phase will be reformed to ⁇ 1 phase.
• the degree of modification of the ⁇ phase is affected by the amounts of Si and P, the amounts of Al, Fe, and Sn, the value of the compositional relation f1, and the amount of ⁇ phase, and is further affected by the average cooling rate from 500°C to 300°C during the cooling process after solidification, the cooling rate at 500°C, and the starting temperature of the cooling treatment. If the cooling treatment start temperature is 700°C or higher, the proportion of the ⁇ phase increases, and the modification of the ⁇ phase may be insufficient.
• the preferred cooling treatment start temperature is lower than 700°C, more preferably 650°C or lower.
• the cooling rate is 300°C/min or lower or the cooling treatment start temperature is 500°C or lower when the temperature of the casting is 500°C, the ⁇ phase is not modified. If the cooling treatment start temperature is preferably 530°C or higher, more preferably 550°C or higher, the ⁇ phase is further modified, and the dezincification corrosion resistance and machinability of the alloy are improved.
• the ⁇ phase will not be modified.
• the average cooling rate in the temperature range from 500°C to 300°C is at least 300°C/min or more, preferably 600°C/min or more, and more preferably 900°C/min or more.
• the ⁇ phase becomes a more modified ⁇ 1 phase, and the dezincification corrosion resistance and machinability become better.
• the upper limit of the cooling rate at 500°C and the average cooling rate in the temperature range from 500°C to 300°C is sufficient to be performed with normal production equipment, and is not particularly specified, but if mentioned, the cooling rate is preferably about 9000°C/min or less.
• ingots made from castings are sometimes used as the raw material for castings, but the modification of the ⁇ phase is not affected by the thermal history of the raw materials used. Whether or not the ⁇ phase is modified is determined during the cooling process after the final casting solidifies.
• Cool Treatment In the production of castings, it is sometimes difficult to cool the casting after casting at a cooling rate of more than 300° C./min at 500° C., and to cool the casting at an average cooling rate from 500° C. to 300° C. at a rate of more than 300° C./min.
• the ⁇ phase of such castings can be modified by subjecting them to heat treatment.
• the casting is heated at a temperature higher than 520°C and lower than 650°C for 1 minute to 5 hours, and then a cooling treatment is initiated at a temperature lower than 650°C and higher than 520°C, so that when the temperature of the casting reaches 500°C, the cooling rate exceeds 300°C/min, and the casting is cooled at an average cooling rate exceeding 300°C/min in the temperature range from 500°C to 300°C, thereby reforming the ⁇ phase to the ⁇ 1 phase.
• the heating temperature during the heat treatment and the cooling treatment start temperature are preferably 540°C or higher, and more preferably 550°C or higher.
• the cooling treatment start temperature is higher than 650°C, the proportion of the ⁇ 1 phase increases, and the dezincification corrosion resistance and impact properties deteriorate, so that it is preferably 620°C or lower.
• the upper limits of the cooling rate at 500°C and the average cooling rate in the temperature range from 500°C to 300°C are sufficient if they can be achieved using normal production equipment, and are not particularly specified. However, if one dares to mention it, the cooling rate is preferably about 9000°C/min or less.
• This manufacturing method produces the free-cutting copper alloy castings according to the first to third embodiments of the present invention.
• the free-cutting copper alloy castings according to the first to third embodiments of the present invention configured as described above, have the alloy composition, compositional formula, metal structure, structure-structure formula, and structure-composition formula specified as described above, so that even with a low Pb content, they can have excellent machinability, good dezincification corrosion resistance, high strength, and good impact properties.
• a copper alloy sand casting trial was carried out using a low frequency melting furnace in actual operation.
• some of the samples were heat-treated in the laboratory.
• the alloy compositions are shown in Tables 5 to 7.
• the manufacturing steps are shown in Tables 8 to 11. In the compositions, "Mm” stands for misch metal and indicates the total amount of rare earth elements. Each manufacturing step is described below.
• Process A Actual machine manufacturing, sand casting (Process No. A1 to A6, A11H to A14H) About 400 kg of raw materials were charged into a low-frequency melting furnace with an internal volume of 1 ton that was actually in operation, and melted at 1,080°C. The raw materials were transferred to a ladle and poured into a sand mold (made of silica sand to which resin had been added) at about 970°C to obtain the type A test material described in JIS H 5120, Section 7.2.
• the cast product was cooled at a cooling rate of about 30°C/min, and when the temperature of the cast product reached 650°C or 750°C, the cast product of the A-type specimen was removed from the sand mold and allowed to cool naturally.
• the cast product removed from the sand mold was cooled at an average cooling rate of 35°C/min, and then the cooling treatment was started at 460°C to 720°C, and the average cooling rate from 500°C to 300°C was adjusted to 20°C/min, 210°C/min, 420°C/min, 660°C/min, 780°C/min, or 900°C/min.
• the average cooling rate from the cooling treatment start temperature to 500°C was adjusted to be the same as the average cooling rate from 500°C to 300°C.
• the cooling treatment start temperature was 550°C or higher, the average cooling rate from 550°C to 500°C was measured, and when the cooling treatment start temperature of the cast product was lower than 550°C, the average cooling rate from the cooling treatment start temperature to 500°C was measured.
• Process No. A12H the average cooling rate from the time after removal from the casting to 460°C was 35°C/min, and the average cooling rate from 460°C to 300°C was 660°C/min.
• Process No. A14H the average cooling rate from the time after removal from the casting to 500° C. was 35° C./min, and the average cooling rate from 500° C. to 300° C. was 20° C./min. Cooling methods adopted included natural air cooling, forced air cooling, shower water cooling, water cooling, simple heat retention, etc.
• Temperature measurements were mainly performed using a radiation thermometer, with a contact thermometer also used in some cases, to measure the temperature of the casting from the time the casting of the A-type specimen was removed from the sand mold until it reached 300°C.
• the radiation thermometer used for temperature measurements was Model IGA8Pro/MB20 manufactured by LumaSense Technologies Inc.
• the A-type specimen obtained was then subjected to metallurgical microscope observation, cutting test, dezincification corrosion test, hardness test, and impact test.
• Process B Laboratory production, metal mold casting (Process No. B1 to B5, B11H to B14H) In a laboratory, raw materials were melted at a specified ratio. In consideration of actual operation, unavoidable impurities such as Fe were intentionally added to some samples. The molten metal at about 950°C was then poured into an iron mold with an inner diameter of 40 mm and a depth of 200 mm. Considering actual casting, when the casting reached about 750°C, the sample was removed from the mold and cooled at a cooling rate of about 60°C/min, and then the cooling treatment was started in the temperature range of 730°C to 470°C.
• the average cooling rate in the temperature range of 500°C to 300°C was changed to 1200°C/min, 1020°C/min, 900°C/min, 480°C/min, 240°C/min, or 40°C/min, and the sample was cooled to room temperature.
• the cooling rate at 500°C i.e., the average cooling rate from 550°C or the cooling treatment start temperature to 500°C, was adjusted to be approximately the same as the average cooling rate from 500°C to 300°C.
• the average cooling rate from the time after removal from the casting to 470°C was 60°C/min, and the average cooling rate from 470°C to 300°C was 900°C/min.
• the average cooling rate from the time after removal from the casting to 500° C. was 45° C./min, and the average cooling rate from 500° C. to 300° C. was adjusted to 40° C./min.
• temperature measurement the temperature of the casting was measured using a combination of a radiation thermometer and a contact thermometer, and the average cooling rate in each temperature range was adjusted to a predetermined value. The obtained metal mold casting was then subjected to metallurgical microscope observation, cutting test, dezincification corrosion test, hardness test, and impact test.
• Process C Continuous casting (Process No. C1 to C3, C11H) About 900 kg of raw materials were charged into a low-frequency melting furnace with an internal volume of 2 tons that was actually in operation, and melted at 1080°C. The molten metal in the holding furnace at 1010°C was passed through the mold of the continuous casting equipment to produce a continuously cast rod with a diameter of 21 mm at a casting speed of 200 mm/min. Cooling was performed by water cooling the mold itself, air cooling, or by installing a shower at an appropriate position from the mold and directly water cooling the continuously cast rod with the shower. The shower position and the amount of water showered were adjusted. Regarding temperature measurement, the temperature of the continuously cast rod was measured using a radiation thermometer and a contact thermometer in combination.
• the cooling rate at 500°C was adjusted to be the same as the average cooling rate from 500°C to 300°C, and was set to 900°C/min, 660°C/min, 480°C/min, or 60°C/min. In this method, the cooling treatment start temperature is not particularly specified.
• the obtained continuously cast rods were subjected to metallurgical microscope observation, cutting test, dezincification corrosion test, hardness test, and impact test.
• Process G Heat treatment (Process No. G1 to G3, G11H to G14H) In process G, some of the sand castings and metal mold castings produced in processes A, B, and C were further heat-treated. The sand castings, metal mold castings, and continuous cast rods produced in processes A14H, B11H, and C11H were further heat-treated. The heating was performed under the conditions of 580° C. and held for 20 minutes. In steps G1, G2, and G3, after heating, the cooling treatment was started at 575° C., and the average cooling rates from 550° C. to 500° C. and from 500° C. to 300° C. were the same, 1200° C./min. In process No.
• the cooling treatment start temperature was 470°C
• the average cooling rate from 580°C to 470°C was 50°C/min
• the average cooling rate from 470°C to 300°C was 900°C/min. did.
• Process No. G13H and G14H after heat treatment at 580°C, no special cooling treatment was performed, and the average cooling rate from 500°C to 300°C was 25°C/min.
• the specimens were subjected to cutting tests, dezincification corrosion tests, hardness tests, and impact tests.
• a rod of ⁇ 40 mm was prepared from free-cutting brass C3604 containing 3 mass% Pb, and was designated as alloy X. Also, an ingot of casting brass CAC203 containing 2 mass% Pb was prepared and designated as alloy Y. The alloy was melted and cast in the same manner as in step No. B1 and step No. B11H, and a die casting of ⁇ 40 mm and length 200 mm was obtained. Alloys X and Y are both commercially available. These alloys were subjected to metallurgical microscope observation, cutting test, dezincification corrosion test, hardness test, and impact test.
• Each test material casting was cut parallel to the longitudinal direction.
• the surface was then polished to a mirror finish and etched with a mixture of hydrogen peroxide and aqueous ammonia.
• an aqueous solution was used that was a mixture of 3 mL of 3 vol% hydrogen peroxide and 22 mL of 14 vol% aqueous ammonia.
• the polished metal surface was immersed in this aqueous solution for approximately 2 to 10 seconds at room temperature of approximately 15 to 25°C. Note that when the ⁇ 1 phase is present, corrosion resistance is improved compared to when the ⁇ phase is present, so the immersion time for etching had to be longer, at 5 to 10 seconds.
• each phase ( ⁇ phase, ⁇ phase, ⁇ 1 phase, ⁇ phase) was manually filled in using the image processing software "Photoshop CC". To distinguish between ⁇ phase and ⁇ 1 phase, if one or more grain boundaries of the ⁇ phase were observed in one field, all ⁇ phases in that field were filled in as ⁇ 1 phase. Next, the images were binarized using the image analysis software "WinROOF2013" to determine the area ratio of each phase.
• the average area ratio of the five fields was calculated for each phase, and the average value was used as the phase ratio of each phase.
• Compounds containing P and Si, precipitates, oxides, Pb or Bi particles, sulfides, and crystallized materials were excluded, and the total area ratio of all constituent phases was set to 100%.
• Non-metallic oxides and sulfides were frequently observed in the cast specimens compared to hot extrusion bars made in mass production facilities.
• a grain boundary pattern i.e., a crystal grain boundary
• the ⁇ phase is regarded as a ⁇ 1 phase and is distinguished from a normal ⁇ phase.
• the crystal grain boundary refers to a linear pattern that penetrates the ⁇ 1 phase crystal grains observed in the ⁇ 1 phase, as shown in Figure 1A.
• P and Si compounds and precipitates may exist in the metal structure.
• P compounds when the amount of P was 0.06 mass% and the average cooling rate from 500°C to 300°C was 15-60°C/min, approximately 250-500 P compounds were observed in a field of view at 500x magnification (80mm x 120mm when printed). However, in the printed metal structure, it is difficult to distinguish between P compounds and compounds of Fe, Mn, Cr, Al, P or Si, Pb particles, oxide particles, etc.
• FE-SEM field emission scanning electron microscope
• JSM-7000F manufactured by JEOL Ltd.
• EDS Electronic Back Scattering Diffracton Pattern
• the machinability test using a lathe was evaluated by a cutting test using a lathe as described below.
• the A-type test material obtained by sand casting in step A, the metal mold casting obtained in step B, the continuous cast rod obtained in step C, and the heat-treated material in step G were first cut to produce test materials with a diameter of 18 mm.
• a K10 carbide tool (chip) without a chip breaker was attached to a lathe.
• the circumference of the test material with a diameter of 18 mm was cut under dry conditions under two conditions: rake angle: 0°, nose radius: 0.4 mm, relief angle: 6°, cutting speed: 40 m/min or 110 m/min, cutting depth: 1.0 mm, and feed rate: 0.11 mm/rev.
• the effect of the cutting speed was also investigated.
• the signals emitted from a three-part dynamometer (AST-type tool dynamometer AST-TL1003, manufactured by Miho Electric Manufacturing Co., Ltd.) attached to the tool were converted into electrical voltage signals and recorded on a recorder. These signals were then converted into cutting resistance (principal force, feed force, thrust force, N).
• cutting tests were carried out in the following order: A ⁇ B ⁇ C ⁇ ..., ... ⁇ C ⁇ B ⁇ A, with the sample names corresponding to the test numbers designated A, B, C, ..., and the test sequence was carried out twice, with each sample being measured four times.
• the cutting resistance is the largest due to the principal force, and the magnitude of the principal force determines the cutting resistance to a large extent. Therefore, the principal force was used as the cutting resistance, and the average value of four measured values was calculated to determine the cutting resistance.
• the cutting resistance (principal force) of a commercially available free-cutting brass bar C3604 (Alloy X, ⁇ 40 mm) made of a Zn-59 mass%Cu-3 mass%Pb-0.2 mass%Fe-0.3 mass%Sn alloy was taken as 100, and the relative value of the cutting resistance of the sample (machinability index) was calculated and a relative evaluation was performed. In other words, the higher the machinability index, the lower the cutting resistance and the better the machinability.
• Cutting resistance depends on the shear strength or tensile strength of the material, and the stronger the material, the higher the cutting resistance tends to be. For example, in the case of a copper alloy that has the same machinability as C3604 but is about 1.2 times stronger than C3604, the cutting resistance is about 20% higher than C3604. For this reason, in the case of a copper alloy with high strength, if the cutting resistance is about 40% higher than C3604, it is considered to be good for practical use.
• the Vickers hardness is about 1.2 times and 1.4 times higher than the extruded bar material of C3604 and the casting of CAC203 containing 2% Pb, so the evaluation standard for machinability in this embodiment was evaluated with a machinability index of 70 as the boundary (boundary value).
• the machinability index is 78 or more, it is evaluated as having excellent machinability (rating: A, excellent) and approximately the same machinability as C3604. If the machinability index was 70 or more and less than 78, the machinability was evaluated as good (evaluation: B, good). If the machinability index was 63 or more and less than 70, the machinability was evaluated as fair (evaluation: C, fair). If the machinability index was less than 63, the machinability was evaluated as poor (evaluation: D, poor). In this application, the aim was to achieve good machinability, so a machinability index of 70 or more was considered to be acceptable.
• Dezincification corrosion test ISO6509 dezincification corrosion test
• the dezincification corrosion test was performed according to the ISO 6509 dezincification corrosion test. This test method is adopted in many countries and is also specified in the JIS standard, JIS H 3250.
• the procedure for the dezincification corrosion test was as follows: first, the test material was embedded in a phenolic resin material, the surface of the sample was polished with emery paper up to grit size 1200, then ultrasonically cleaned in pure water and dried. Each sample was immersed in an aqueous solution (12.7 g/L) of 1.0% cupric chloride dihydrate (CuCl 2 .2H 2 O) and held for 24 hours under a temperature condition of 75° C.
• aqueous solution (12.7 g/L) of 1.0% cupric chloride dihydrate (CuCl 2 .2H 2 O)
• the sample was taken out of the aqueous solution.
• the specimen was re-embedded in phenolic resin.
• the specimen was then cut so that the cross section of the corroded area was the longest cut.
• the specimen was then polished. Using a metallurgical microscope, the dezincification corrosion depth was observed at 10 points in the field of view of the microscope at a magnification of 100 to 500. The deepest corrosion point was recorded as the maximum dezincification corrosion depth.
• the maximum corrosion depth is about 500 ⁇ m or more.
• the maximum corrosion depth is less than 250 ⁇ m, which is 50% less than the maximum corrosion depth of C3604 or CAC203, it is evaluated as having good dezincification corrosion resistance in practical use (evaluation: B, good).
• the maximum corrosion depth is 100 ⁇ m or less, it is evaluated as having excellent dezincification corrosion resistance in practical use (evaluation: A, excellent).
• the dezincification corrosion resistance is equivalent to, or in some cases worse than, C3604 or CAC203, and therefore the dezincification corrosion resistance is not maintained and is rated as "D" (poor).
• the maximum corrosion depth is 250 ⁇ m or more and 400 ⁇ m or less, the dezincification corrosion resistance is rated as fair (rating: C, fair).
• good (rating: B, good) and excellent (rating: A, excellent) were deemed to be acceptable.
• the impact test was carried out in the following manner. U-notch test pieces (notch depth 2 mm, notch bottom radius 1 mm) according to JIS Z 2242 were taken. A Charpy impact test was carried out using an impact blade with a radius of 2 mm to measure the impact value. In order to maintain good toughness and impact properties, the Charpy impact test value is preferably 25 J/ cm2 or more, more preferably 30 J/ cm2 or more.
• the decrease in machinability and dezincification corrosion resistance is considered to be due to the fact that Fe, Mn, etc., combine with a part of Si and P to form intermetallic compounds of Fe, Mn, etc. with Si and P.
• the compounds of Fe, etc. with Si and P exist and the effective Si concentration and P concentration are reduced, resulting in the deterioration of machinability and corrosion resistance (Alloy Nos. S02, S38, S39, S63, etc.).
• compositional relationship f1 When the compositional relationship f1 was less than 57.3, the ⁇ phase was not modified or was modified insufficiently, resulting in poor dezincification corrosion resistance and poor machinability in high-speed cutting. When the compositional relationship f1 was greater than 60.8, the area ratio of the ⁇ 1 phase was small and machinability was poor (Alloy Nos. S57 and S53). When the value of the compositional relationship f1 was 57.3 or more, the ⁇ phase was modified, improving dezincification corrosion resistance and machinability, and at 58.0 or more, it was even better.
• machinability is roughly saturated when the amount of ⁇ 1 phase (f4) is 45 to 60% and the amount of Si is 1 mass% (e.g. Alloy Nos. S02, S12, Process Nos. A1 and A2, etc.). 14) When the amount of ⁇ phase (f4A) that was not modified to ⁇ 1 phase was 45 or more and f6A exceeded 40, the dezincification corrosion depth was large and the machinability, especially at high speeds, was poor (Test Nos. S22, S106, S223, etc.).
• the cooling rate at 500°C: approximately 300°C/min, and the average cooling rate from 500°C to 300°C: approximately 300°C/min are the boundary values for whether or not grain boundaries are observed in the ⁇ phase, i.e., whether or not the ⁇ phase is modified.
• the machinability and dezincification corrosion resistance at high speeds changed drastically (Process Nos. A4, A13, B3, B14H, etc.).
• the cooling treatment start temperature was higher than 700°C
• the proportion of ⁇ 1 phase increased, the machinability index was slightly lower, the machinability at high speeds was particularly poor, and the dezincification corrosion resistance was also poor.
• the proportion of ⁇ 1 phase exceeded 80%, the ⁇ phase was sometimes not modified.
• the dezincification corrosion was a selective corrosion of the ⁇ 1 phase, and the rate of dezincification corrosion seemed to be slightly increased when the proportion of ⁇ 1 phase was high (Process Nos. A1 to A6, A11H, B1 to B5, B12H, etc.).
• the average cooling rate from 500°C to 300°C was about 200-250°C/min, no grain boundaries were observed in the ⁇ phase, and in many cases, small amounts of P compounds were present.
• the machinability, especially at 110 m/min was deteriorated, and the dezincification corrosion resistance was deteriorated (Process Nos. A13H, B14H, etc.).
• the ⁇ phase is modified by cooling at a rate of more than 300°C/min from 550°C to 500°C and at an average cooling rate of more than 300°C/min in the temperature range from 500°C to 300°C, and the dezincification corrosion resistance and machinability are significantly improved (Process Nos. C1 to C3, C11H). 22) After casting, even when a cooling process was performed at a high cooling rate from a high temperature exceeding 500°C, no cracks were observed in the castings (Process Nos. A1 to A6, B1 to B5, and C1 to C3).
• the alloy of this embodiment in which the content of each added element, the compositional relationship formula, and each structural relationship formula are within the appropriate range, has good machinability, dezincification corrosion resistance, and mechanical properties. Furthermore, in order to obtain excellent properties in the alloy of this embodiment, the cooling conditions after casting and the heat treatment conditions can be set within the appropriate range.
• the free-cutting copper alloy casting of this embodiment has a small Pb content, is excellent in machinability, dezincification corrosion resistance, and castability, and has high strength and good impact properties. Therefore, the free-cutting copper alloy of this embodiment is suitable for appliances and parts related to drinking water and sanitary facilities, food appliances, electric and home appliance parts, automobile parts, machine parts, stationery, toys, musical instruments, sliding parts, instrument parts, precision machine parts, medical parts, water meters, and parts related to liquids and gases such as industrial water, wastewater, and hydrogen.
• the present invention can be suitably applied as a component material for items used in the aforementioned fields under the names of water taps, hot and cold water mixing taps, stop valves, water meters, shower heads, valves, joints, cocks, gears, axles, bearings, shafts, sleeves, spindles, sensors, bolts, nuts, connectors, and the like.

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